The present invention relates generally to acoustical wave generators, and more particularly to an acoustic wave generator for producing audible sound waves.
An acoustic wave is formed when fluid pressure, be it for gas (air or other gas) or liquid, is made to vary in time and space. This is usually effected through a device which vibrates to cause this pressure wave. In air, this is typically done with a vibrating diaphragm in a device known as a loudspeaker, which alternately compresses and rarefies the air contacting the diaphragm as it vibrates.
An exemplary prior art loudspeaker is depicted in FIG. 1. In this device, the diaphragm vibrates in a range typically between 20 Hz to 20,000 Hz to create audible sound and at even higher frequencies to produce inaudible ultrasound. An applied current through the voice coil causes a deflection proportional to the current through magnetic interaction between the voice coil and magnet. As the diaphragm is caused to deflect to the right, air is compressed; as it is caused to deflect to the left, air is rarefied. This creates a pressure wave travelling away from the diaphragm which we perceive as sound.
The principle works similarly for other media, such as liquid or even solids. Also, actuation is not limited to magnetic means as shown here. For example, electrostatic or piezoelectric forces are routinely used for the same purpose. Note that a loudspeaker is a zero net mass flux device, as it does not cause a net positive mass flow of the surrounding medium.
While this method of sound reproduction is effective and widely used, its ability to deliver acoustic power remains dependent on the size of the diaphragm as well as the amount or speed of diaphragm deflection possible. These dependencies become a problem when higher acoustic power is desired per given size. This is the case when miniaturization demands delivery of adequate power at increasingly smaller device sizes such as is the case with cell phones and laptop computers. In particular, such dependencies limit the possible miniaturization of speakers.
The present invention is therefore directed to the problem of developing a method and apparatus for reproducing sound with sufficient acoustic power for consumer electronic applications but in an extremely compact size.